Conventional mailers are a series of connected, stuffed, sealed envelopes which are made from continuous webs of paper by a forms manufacturer. Information common to all of the envelope assemblies are printed on the webs. These assemblies are zig-zag folded and shipped to a large user who employs computerized impact printers to print the name of the recipient on the envelope and to enter certain confidential entries through the envelope onto the interior plies. The assemblies are separated one from another and mailed to customers. A basic mailer is described in U.S. Pat. No. 3,104,799 to Steidinger. Other variations are described in U.S. Pat. Nos. 4,095,695 to Steidinger and 4,102,251 to Steidinger. During manufacture of mailer assemblies, glue lines, dots, or patterns are applied along the open edges of the mailer forms to seal the envelope. The glue application operation is messy at times, especially at the beginning and during any stoppage.
More recently, there has been a need for a mailer form in business system and promotional applications, using a single message-ply processed by non-impact printers, such as a laser printer. The ply is then folded and glued along open edges to become a mailer. Several types of laser mailers are disclosed in U.S. Pat. Nos. 4,754,915 to Steidinger, 4,889,278 to Steidinger, 4,944,449 to Schmidt, and 5,095,682 to Steidinger, the disclosures of which are hereby incorporated by reference.
Laser mailers are designed to be processed by advanced, computer-controlled, non-impact laser printers. In the printer, a laser beam of light produces a latent electrostatic image on photoconductor cylinder or drum. As the cylinder or drum is rotated, the negatively charged toner particles jump from the magnetic brush to the positively charged parts of the photoconductor cylinder due to electrostatic interaction. The imaged photoconductor cylinder continues to rotate and transfer the toner particles to a paper web which has been positively charged higher than that of the photoconductor cylinder by a transmission corona. The toner image on the paper is then fused into the paper by passage through a pair of rolls which provide heat and pressure to form bonded images on the paper web.
An untreated surface of a paper web has poor receptivity for the fused toner particles, and the images may be rubbed off totally or partially. When used for printing security documents, addresses, prices, bar codes, identification numbers, serial numbers, invoices, etc., the laser printing may become illegible or the object of fraud.
Several prior patents have disclosed various means to enhance toner anchorage to substrates. For example, U.S. Pat. No. 2,855,324 to Van Dorn discloses coatings of thermoplastic resin having melting points between 150.degree. F. and 300.degree. F. (such as polyethylenes, polyamides, and polystyrene) to improve xerographic toner transfer. U.S. Pat. No. 3,130,064 to Insalaco discloses coating a record card with a film by immersing in a thermoplastic solution, such as a toluene solution of styrene-n-butylmethacrylate copolymer, to improve xerographic toner adhesion. U.S. Pat. No. 4,254,201 to Sawai et al. discloses use of porous aggregates which contain encapsulated pressure-sensitive adhesive as individual granules and pigment particles in the interstices between the granules to improve the toner adhesion on the substrate for use in electrostatic photography. U.S. Pat. No. 4,499,168 to Mitsuhashi discloses addition of vinyl-type polymer to toner particles to improve the adhesion in a xerographic process. U.S. Pat. No. 4,510,225 to Kuehnle et al. discloses coating thermoplastic polymer, such as polyester, polyacrylate, polyvinyl buryral, polyvinyl formal, polyvinyl acetate, copolymer of vinyl acetate-vinyl chloride, copolymer of vinylidene chloride acrylonitrile, polyethylene, and polypropylene, on a substrate to enhance the toner adhesion in electrostatic reproduction. U.S. Pat. No. 5,045,426 to Maierson et al. discloses coating a cellulosic web product with a copolymer of styrene and acrylic acid having a glass transition temperature of between about -16.degree. and 22.degree. C. to enhance laser toner adhesion, and the toner is fused to the web surface by the application of heat and pressure.
During manufacture, the laser printed ply is folded and glued to form a mailer. Glue applicators are used to lay down continuous glue lines in the vertical margins (i.e., longitudinal margins) of the mailer form and dot patterns (or lines) of glue in places across the width (i.e., latitudinal margins) to seal the laser mailer. However, as is the case with impact printed mailers, problems with glue application exist in the production of laser mailers. To prevent the water-based glue from overflowing, glue lines are applied off the open edges, resulting in slightly open margins after the mailer is sealed.